Pixel driving chip, driving method thereof, and pixel structure

ABSTRACT

The present application discloses a pixel driving chip for compensating an original signal provided to a pixel structure including a driving transistor having a drain electrode coupled to a light-emitting device, the pixel driving chip includes a control circuit configured to generate at least one control voltage signals for controlling the driving transistor; an acquisition circuit configured to acquire a measured source voltage at a source electrode of the driving transistor under control of the at least one control voltage signals; a computation circuit configured to compute a compensation voltage based on the measured source voltage; a storage circuit configured to store the compensation voltage; a compensation circuit configured to compensate the original signal provided to the driving transistor using the compensation voltage stored in the storage circuit to obtain a compensated signal; and an output circuit configured to output the compensated signal to the driving transistor.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Chinese Patent Application No.201610073383.4, filed Feb. 2, 2016, the contents of which areincorporated by reference in the entirety.

TECHNICAL FIELD

The present invention relates to a pixel driving technique, moreparticularly to a pixel driving chip, a driving method thereof, and apixel structure.

BACKGROUND

Organic Light Emitting Display (OLED) apparatuses are self-emittingapparatuses having many advantageous features including a low drivingvoltage, a high light emission efficiency, a short response time, highclarity and high contrast in displayed image, near-180° viewing angle,and a wide range of operational temperatures. OLED apparatuses may bedivided into two categories, a passive matrix type OLED and an activematrix type OLED (AMOLED).

SUMMARY

In one aspect, the present invention provides a pixel driving chip forcompensating an original signal provided to a pixel structure includinga driving transistor having a drain electrode coupled to alight-emitting device, the pixel driving chip comprising a controlcircuit configured to generate at least one control voltage signals forcontrolling the driving transistor; an acquisition circuit configured toacquire a measured source voltage at a source electrode of the drivingtransistor under control of the at least one control voltage signals; acomputation circuit configured to compute a compensation voltage basedon the measured source voltage; a storage circuit configured to storethe compensation voltage; a compensation circuit configured tocompensate the original signal provided to the driving transistor usingthe compensation voltage stored in the storage circuit to obtain acompensated signal; and an output circuit configured to output thecompensated signal to the driving transistor for driving thelight-emitting device.

Optionally, the original signal is one of a gate scanning signalprovided to a gate electrode of the driving transistor and a data signalprovided to the source electrode of the driving transistor.

Optionally, the pixel driving chip further comprises a trigger circuitconfigured to trigger operations of the acquisition circuit, thecomputation circuit, and the storage circuit during powering up of thepixel structure for image display; and a shutdown circuit configured toshut down the acquisition circuit, the computation circuit, and thestorage circuit after the compensation voltage is computed and stored.

Optionally, the compensated signal is a compensated gate scanningsignal, and the output circuit is configured to output the compensatedgate scanning signal to a gate electrode of the driving transistor forimage display; and the compensation voltage is a threshold voltage ofthe driving transistor, wherein the at least one control voltage signalscomprises a first test signal V1 outputted to a gate electrode of thedriving transistor to control the driving transistor to be in theconducting state and a second test signal V2 outputted to a drainelectrode of the driving transistor to control the driving transistor,the threshold voltage being a difference between the measured sourcevoltage and the first test signal V1.

Optionally, the control circuit is configured to generate the at leastone control voltage signals multiple times, each time the at least onecontrol voltage signals comprises a set of first test signal V1 andsecond test signal V2, thereby generating a plurality sets of first testsignal V1 and second test signal V2 having different voltage values; thestorage circuit is configured to store a threshold voltage correspondingto each set of the plurality sets of control voltage signals; and thecompensation circuit is configured to determine a matched set out of theplurality sets of first test signal V1 and second test signal V2 thatmatches with the original signal, and is configured to compensate theoriginal signal using the threshold voltage corresponding to the matchedset to obtain the compensated signal.

Optionally, the second test signal V2 of the matched set is one that isclosest to a calculated drain voltage corresponding to the originalsignal, among a plurality of second test signals V2 of the pluralitysets of first test signal V1 and second test signal V2.

Optionally, the compensated signal is a compensated data signal, and theoutput circuit is configured to output the compensated data signal tothe source electrode of the driving transistor for image display; andthe compensation voltage is a voltage drop at the source electrode ofthe driving transistor relative to a reference voltage Vdd, wherein theat least one control voltage signals comprises a third test signal V3outputted to a gate electrode of the driving transistor to control thedriving transistor to be in a blocking state and the reference voltageVdd applied to the source of the driving transistor, the voltage dropbeing a difference between the measured source voltage of the drivingtransistor and a reference source voltage value.

Optionally, the reference source voltage value is one of a maximum valueand a minimum value among all measured source voltages of all drivingtransistors in all pixel structures.

Optionally, the driving transistor is a P-type transistor and the thirdtest signal V3 is multiplexed as the reference voltage Vdd.

Optionally, the at least one control voltage signals further comprise afourth test signal V4 applied to the drain electrode of the drivingtransistor for discharging cathode voltage of the light-emitting device.

In another aspect, the present invention provides a method of driving apixel structure including a driving transistor having a drain electrodecoupled to a light-emitting device, comprising generating at least onecontrol voltage signals to control the driving transistor; acquiring ameasured source voltage at a source electrode of the driving transistorunder control of the at least one control voltage signals; computing acompensation voltage based on the measured source voltage; storing thecompensation voltage; compensating an original signal provided to thedriving transistor using the compensation voltage to obtain acompensated signal; and outputting the compensated signal to the drivingtransistor.

Optionally, the original signal comprises one or both of a gate scanningsignal provided to a gate electrode of the driving transistor and a datasignal provided to the source electrode of the driving transistor.

Optionally, the method further comprises triggering processes ofacquiring the measured source voltage, computing the compensationvoltage based on the measured source voltage, and storing thecompensation voltage during powering up of the pixel structure for imagedisplay; and ending the processes of acquiring the measured sourcevoltage, computing the compensation voltage based on the measured sourcevoltage, and storing the compensation voltage after the compensationvoltage is computed and stored.

Optionally, the compensated signal is a compensated gate scanningsignal, and the output circuit is configured to output the compensatedgate scanning signal to a gate electrode of the driving transistor forimage display; and the compensation voltage is a threshold voltage ofthe driving transistor, wherein the at least one control voltage signalscomprises a first test signal V1 outputted to a gate of the drivingtransistor to control the driving transistor to be in the conductingstate and a second test signal V2 outputted to a drain electrode of thedriving transistor to control the driving transistor, the thresholdvoltage being a difference between the measured source voltage and thefirst test signal V1.

Optionally, generating the at least one control voltage signalscomprises generating the at least one control voltage signals multipletimes, each time the at least one control voltage signals comprises aset of first test signal V1 and second test signal V2, therebygenerating a plurality sets of first test signal V1 and second testsignal V2 having different voltage values; storing the compensationvoltage comprises storing a threshold voltage value corresponding toeach control voltage signal; and compensating the original signalcomprises determining a matched set out of the plurality sets of firsttest signal V1 and second test signal V2 that matches with the originalsignal; and using the threshold voltage corresponding to the matched setto compensate the original signal to obtain the compensated signal.

Optionally, the second test signal V2 of the matched set is one that isclosest to a calculated drain voltage corresponding to the originalsignal, among a plurality of second test signals V2 of the pluralitysets of the first test signal V1 and the second test signal V2.

Optionally, the compensated signal is a compensated data signal, and theoutput circuit is configured to output the compensated data signal tothe source electrode of the driving transistor for image display; andthe compensation voltage is a voltage drop at the source electrode ofthe driving transistor relative to a reference voltage Vdd, wherein theat least one control voltage signal comprises a third test signal V3outputted to a gate of the driving transistor to control the drivingtransistor to be in a blocking state and the reference voltage Vddapplied to the source of the driving transistor, the voltage drop beinga difference between the measured source voltage of the drivingtransistor and a reference source voltage value.

Optionally, the reference source voltage value is one of a maximum valueand a minimum value among all measured source voltages of all drivingtransistors in all pixel structures.

Optionally, the driving transistor is a P-type transistor and the thirdtest signal V3 is multiplexed as the reference voltage Vdd.

Optionally, the control voltage signal further comprises a fourth testsignal V4; the method of driving the pixel structure further comprisingdischarging cathode voltage of the light-emitting device by applying thefourth test signal V4 to the drain of the driving transistor.

In another aspect, the present invention provides a display apparatus,comprising a pixel driving chip described herein; and a pixel structurecomprising a light-emitting device; a driving transistor having thedrain electrode coupled to the light-emitting device; and astate-control unit configured to be coupled between the pixel drivingchip and the driving transistor for controlling the driving transistorupon receiving the at least one control voltage signals from the pixeldriving chip; wherein the driving transistor is configured to receivethe compensated signal for image display obtained by compensating theoriginal signal with the compensation voltage; the compensation voltageis computed based on a measured source voltage acquired at a sourceelectrode of the driving transistor under control of the at least onecontrol voltage signals.

Optionally, the original signal is one of a gate scanning signalprovided to a gate electrode of the driving transistor and a data signalprovided to the source electrode of the driving transistor.

Optionally, the compensated signal is a compensated gate scanningsignal, and the output circuit is configured to output the compensatedgate scanning signal to a gate electrode of the driving transistor; thecompensation voltage is a threshold voltage of the driving transistor,wherein the at least one control voltage signals comprises a first testsignal V1 and a second test signal V2; and the state-control unitcomprises a first switching unit and a second switching unit, the firstswitching unit having a first terminal configured to be connected to thepixel driving chip for receiving the first test signal V1 and a secondterminal connected to a gate of the driving transistor, the secondswitching unit having a first terminal configured to be connected to thepixel driving chip for receiving the second test signal V2 and a secondterminal connected to a drain electrode of the driving transistor, eachof the first switching unit and the second switching unit having acontrol terminal configured to be coupled to the pixel driving chip forswitching on and off each of the first switching unit and the secondswitching unit, respectively, the threshold voltage of the drivingtransistor being a difference between the measured source voltage andthe first test signal V1.

Optionally, the compensated signal is a compensated data signal, and theoutput circuit is configured to output the compensated data signal tothe source electrode of the driving transistor, the compensation voltageis a voltage drop at the source electrode of the driving transistorrelative to a reference voltage Vdd, wherein the set of control voltagesignals comprises a third test signal V3 and the reference voltage Vdd;and the state-control unit comprises a first switching unit and a thirdswitching unit, the first switching unit having a first terminalconfigured to be connected to the pixel driving chip for receiving thethird test signal V3 and a second terminal connected to a gate of thedriving transistor, the third switching unit having a first terminalconfigured to be connected to the pixel driving chip for receiving thereference voltage Vdd and a second terminal connected to the sourceelectrode of the driving transistor, each of the first switching unitand the third switching unit having a control terminal coupled to thepixel driving chip for switching on and off each of the first switchingunit and the third switching unit, respectively.

Optionally, the driving transistor is a P-type transistor and the thirdtest signal V3 is multiplexed as the reference voltage Vdd.

Optionally, the state control circuit further comprises a fourthswitching unit, the fourth switching unit comprising a thin filmtransistor having a first terminal configured to be connected to thepixel driving chip for receiving a clearing voltage signal V4 fordischarging cathode voltage of the light-emitting device and a secondterminal connected to a drain electrode of the driving transistor, thefourth switching unit having a control terminal configured to beconnected to the pixel driving chip for receiving a control signal forswitching on and off the fourth switching unit.

Optionally, the pixel structure further comprises a fifth switching unithaving a thin film transistor coupled between the drain of the drivingtransistor and a cathode of the light-emitting device, the thin filmtransistor of the fifth switching unit having a control terminalconfigured to be connected to the pixel driving chip for receiving acontrol signal, the control signal being configured to turn off the thinfilm transistor of the fifth switching unit before the set of controlvoltage signals is outputted from the pixel driving chip to the drivingtransistor; and configured to turn on the thin film transistor of thefifth switching unit after the set of control voltage signals isoutputted from the pixel driving chip to the driving transistor.

BRIEF DESCRIPTION OF THE FIGURES

The following drawings are merely examples for illustrative purposesaccording to various disclosed embodiments and are not intended to limitthe scope of the present invention.

FIG. 1 is a simplified block diagram of a pixel driving chip accordingto an embodiment of the present disclosure.

FIG. 2 is simplified block diagram of a pixel driving chip according toanother embodiment of the present disclosure.

FIG. 3 is a circuit diagram of a pixel structure during measurement ofthreshold voltage of a driving transistor according to some embodimentsof the present disclosure.

FIG. 4 is a circuit diagram of a pixel structure during measurement ofvoltage drop across the driving transistor according to some embodimentsof the present disclosure.

FIG. 5 is a flow chart illustrating a method for driving a pixelstructure with a voltage compensation according to an embodiment of thepresent disclosure.

FIG. 6 is a simplified block diagram of a pixel structure according toan embodiment of the present disclosure.

FIG. 7 is a diagram of a pixel structure controlled by a pixel drivingchip operated during a threshold voltage compensation according to anembodiment of the present disclosure.

FIG. 8 is a diagram of a pixel structure controlled by a pixel drivingchip operated during a voltage drop compensation according to anembodiment of the present disclosure.

FIG. 9 is a diagram of a pixel structure controlled by a pixel drivingchip operated for combined threshold voltage and voltage dropcompensation according to an embodiment of the present disclosure.

FIG. 10 is a simplified timing diagram for operating the pixel structureof FIG. 9 according to an embodiment of the present disclosure.

FIG. 11 is a simplified timing diagram for operating the pixel structureof FIG. 9 according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

The disclosure will now describe more specifically with reference to thefollowing embodiments. It is to be noted that the following descriptionsof some embodiments are presented herein for purpose of illustration anddescription only. It is not intended to be exhaustive or to be limitedto the precise form disclosed.

In the active matrix type OLED apparatuses, each image display pixelstructure includes a thin film transistor for driving a light emissiondiode (a.k.a. a driving transistor). The driving transistor has athreshold voltage value that drifts over its operation time. Differentdriving transistors throughout the display apparatus may have differentthreshold voltages. Typically, the threshold voltages of correspondingdriving transistors in the active matrix OLED apparatuses arecompensated to overcome non-uniform image display. Moreover,power-supply voltage has different voltage drops in different pixelsbecause a distance between each pixel structure and the power supplysignal node varies from pixel to pixel. Accordingly, the non-uniformvoltage drops in some display apparatus are also compensated to furtherenhance image display uniformity.

Two compensation modes may be implemented for compensating the thresholdvoltage and the voltage drop associated with each pixel structure. Afirst compensation mode is a circuit compensation mode, in which avoltage-compensation circuit is included in each pixel structure. Asecond compensation mode is a driving compensation mode, in whichvoltages of signals applied to each pixel structure are compensated.

In the driving compensation mode, it is required to determine athreshold voltage of each driving transistor or a voltage drop over eachpixel structure. The signals applied to each pixel structure (e.g., agate scanning signal provided to a gate electrode of the drivingtransistor and a data signal provided to a source electrode of thedriving transistor) are compensated for achieving a more uniform imagedisplay. In conventional driving compensation mode, the thresholdvoltage and the voltage drop of the driving transistor of each pixelstructure are collected via a multiplexed display signal during a normaloperation of the display apparatus. In order to ensure a normal andaccurate image display, all the display signals are determined andcannot be changed. Therefore, the conventional driving compensation modeis disadvantageous because the compensation process is uncontrollableand inflexible.

The present disclosure provides a pixel driving chip, a driving methodthereof, and a pixel structure controlled by the pixel driving chip thatsubstantially obviates one or more of the problems due to limitationsand disadvantages of the related art. In one aspect, the presentdisclosure provides a pixel driving chip for compensating an originalsignal provided to a pixel structure including a driving transistorhaving a drain electrode coupled to a light-emitting device. In someembodiments, the pixel driving chip includes a control circuitconfigured to generate one or more control voltage signals forcontrolling the driving transistor to be in a corresponding testingstate; an acquisition circuit configured to acquire a measured sourcevoltage at a source electrode of the driving transistor under thetesting state corresponding to the one or more control voltage signals;a computation circuit configured to compute a compensation voltage basedon the measured source voltage; a storage circuit configured to storethe compensation voltage; a compensation circuit configured tocompensate the original signal provided to the driving transistor usingthe compensation voltage stored in the storage circuit to obtain acompensated signal; and an output circuit configured to output thecompensated signal to the driving transistor. The control voltagesignals are independent from any working signal for the pixel structure,such as data signal and switching signal, etc. Thus, controlling of thedriving transistor by such control voltage signal to be a certaintesting state is unaffected by normal operations of the pixel structure.Voltage compensation of the original signal may be achieved with greatcontrollability and flexibility.

In a first phase (“threshold voltage measurement phase), the controlcircuit configured to generate at least one control voltage signals forcontrolling the driving transistor to be in a conducting state while thedriving transistor is isolated from a power-supply voltage Vdd. Theoriginal signal is a gate scanning signal provided to a gate electrodeof the driving transistor, the compensated signal is a compensated gatescanning signal, the compensation voltage is a threshold voltage of thedriving transistor, and the output circuit is configured to output thecompensated gate scanning signal to a gate electrode of the drivingtransistor for image display. The at least one control voltage signalsinclude a first test signal V1 outputted to a gate electrode of thedriving transistor and a second test signal V2 outputted to a drainelectrode of the driving transistor to control the driving transistor tobe in a conducting state, while the driving transistor is isolated froma power-supply voltage Vdd, The threshold voltage is a differencebetween the measured source voltage and the first test signal V1

In a second phase (“voltage-drop measurement phase), the control circuitconfigured to generate at least one control voltage signals forcontrolling the driving transistor to be in a blocking state while thedriving transistor is connected to the power-supply voltage Vdd. Theoriginal signal is a data signal provided to the source electrode of thedriving transistor, the compensated signal is a compensated data signal,the compensation voltage is a voltage drop at the source electrode ofthe driving transistor relative to a reference voltage Vdd, and theoutput circuit is configured to output the compensated data signal tothe source electrode of the driving transistor for image display. The atleast one control voltage signals include a third test signal V3outputted to a gate electrode of the driving transistor to control thedriving transistor to be in a blocking state and the reference voltageVdd applied to the source of the driving transistor. The voltage dropbeing a difference between the measured source voltage of the drivingtransistor and a reference source voltage value.

Optionally, the light emitting device is an organic light emittingdiode. Optionally, the light emitting device includes at least a liquidcrystal layer, a common electrode, and a pixel electrode.

Optionally, the original signal includes a gate scanning signal providedto a gate electrode of the driving transistor and a data signal providedto a source electrode of the driving transistor. Optionally, theoriginal signal is a gate scanning signal. Optionally, the originalsignal is a data signal.

In some embodiments, the pixel driving chip is used to generate andoutput one or more voltage excitation signals (i.e., control voltagesignals) for controlling a driving transistor to a corresponding testingstate by at least controlling its gate voltage Vf and its drain voltageVd. Optionally, the pixel driving chip generates a plurality sets ofvoltage excitation signals corresponding to a plurality sets of Vf andVd. Different voltage excitation signals correspond to different Vf andVd values. A source voltage Vs at the source electrode of the drivingtransistor is measured for each set of voltage excitation signalscorresponding to each testing state.

In some embodiments, the original signal is a gate scanning signal, thecompensated signal is a compensated gate scanning signal, and the outputcircuit is configured to output the compensated gate scanning signal toa gate of the driving transistor. Optionally, the compensation voltageis a threshold voltage of the driving transistor. The threshold voltageof the driving transistor, Vth, may be determined based on an equationVs=Vf−Vth. Various threshold voltages Vth at different drain and sourcevoltage conditions (varied by varying the voltage excitation signalsunder control by the pixel driving chip) can be obtained based on themeasured source voltage Vs acquired under these conditions. Accordingly,a compensation voltage for compensating an original signal for drivingthe pixel can be computed.

In some embodiments, the original signal is a data signal, thecompensated signal is a compensated data signal, and the output circuitis configured to output the compensated data signal to the sourceelectrode of the driving transistor. Optionally, the compensationvoltage is a voltage drop at the source electrode of the drivingtransistor relative to a power-supply voltage Vdd. Optionally, the oneor more voltage excitation signals control the driving transistor to bein a blocking state. The voltage drop is determined as a differencebetween the measured source voltage of the driving transistor and areference source voltage value. The reference source voltage value maybe any appropriate value. For example, the reference source voltagevalue may be a maximum value among all measured source voltages of alldriving transistors in all pixel structures. Optionally, the referencesource voltage value is a minimum value among all measured sourcevoltages of all driving transistors in all pixel structures. Optionally,the reference source voltage value is a medium or average value amongall measured source voltages of all driving transistors in all pixelstructures.

In some embodiments, the present disclosure provides a pixel drivingchip configured to output a compensated signal to a pixel structure. Thepixel structure includes at least a light-emitting device coupled ordriven by a driving transistor. Optionally, the light-emitting device isan organic light emitting diode. Optionally, the light-emitting deviceis an active-matrix driven organic light emitting diode. FIG. 1 is asimplified block diagram of a pixel driving chip according to anembodiment of the present disclosure. As shown in FIG. 1, the pixeldriving chip includes a control circuit configured to generate andoutput one or more voltage excitation signals, and provide it to adriving transistor for controlling the transistor state to be a testingstate corresponding to one or more voltage excitation signals. Thesevoltage excitation signals are independent from the work signals such asdata signal and switching signal for operating associated pixelstructure. Further, the pixel driving chip includes an acquisitioncircuit configured to acquire a plurality of measured source voltages atthe source electrode of the driving transistor under a plurality oftesting states. The plurality of testing states correspond to varyinggate voltages and drain voltages of the driving transistor, in responseto varying voltage excitation signals generated by the control circuit.Moreover, the pixel driving chip includes a computation circuitconfigured to compute a compensation voltage based on the measuredsource voltages obtained from the driving transistor under the testingstates.

In some embodiments, the compensation voltage is a threshold voltage ofthe driving transistor. Optionally, the threshold voltage may bedetermined as the difference between a gate voltage and the measuredsource voltage at the source electrode while the source electrode of thedriving transistor is isolated from the power-supply voltage Vdd. Insome embodiments, the compensation voltage is a voltage drop at thesource electrode of the driving transistor relative to a power-supplyvoltage when the driving transistor is kept at an off-state. The normaloperation of the pixel structure for image display may be conductedafter the compensation voltage is obtained. Thus, the acquisition andcomputation of compensation voltage (e.g., the threshold voltage and thevoltage drop) do not affect the normal operation of the pixel structurefor image display. The compensation voltage compensates the thresholdvoltage of the driving transistor, the voltage drop at the source of thedriving transistor relative to the power-supply voltage, or both. Byhaving the present pixel driving chip, effects of variations andnon-uniformity in the threshold voltage or the voltage drop throughoutthe display panel on the image display may be significantly reduced.Higher image display quality with much reduced intensity irregularitiesthroughout the display panel may be achieved.

Referring to FIG. 1, the pixel driving chip further includes a storagecircuit configured to store the compensation voltage and a compensationcircuit configured to compensate the original signal provided to thedriving transistor using the compensation voltage stored in the storagecircuit to obtain a compensated signal. Moreover, the pixel driving chipin FIG. 1 further includes an output circuit configured to output thecompensated signal to the driving transistor for driving thelight-emitting device of the pixel structure for image displaysubstantially free from the effect of threshold voltage Vth drift andnon-uniformity or variation of voltage drop relative to Vdd. As such,the pixel structure displays a pixel image more accurately with lessintensity irregularity. The compensation process described herein willnot affect normal operation of the pixel structure for image display. Asimplified signal line design may be used for signal compensation.

For each pixel structure, the threshold voltage Vth of the drivingtransistor drifts over an elongated time. Typically, the thresholdvoltage stays relatively stable during a relatively short period of time(e.g., a continuous working period such as a week of working time). Whenthe pixel driving chip is in the compensation mode, it takes certaintime and processing resource to obtain the threshold voltage or thevoltage drop. Thus, frequent acquisition of the threshold voltage or thevoltage drop may be time-consuming and take up a large amount ofprocessing resources. Accordingly, in some embodiments, a singlecompensation voltage value may be used for a continuous working periodfor balancing compensation accuracy and consumption of time andprocessing resource. For example, the single compensation voltage valuemay be computed based on the threshold voltage or voltage drop obtainedevery time when the pixel structure is powering up (for intended normalimage display), the single compensation voltage value may be usedthroughout the working period. In some embodiments, a compensationvoltage value may be computed based on the threshold voltage or voltagedrop obtained every time when the pixel structure is shut down, and thecompensation voltage value may be used throughout the working periodwhen the pixel structure is powering up next time. In some embodiments,a compensation voltage value may be obtained between two adjacent framesof image, and the compensation voltage value so obtained may be used forthe next frame of image.

FIG. 2 is simplified block diagram of a pixel driving chip according toanother embodiment of the present disclosure. As shown, the pixeldriving chip of FIG. 2 includes a trigger circuit and a shutdown circuitin combination with the pixel driving chip of FIG. 1. Optionally, thetrigger circuit is configured to trigger operations of the acquisitioncircuit, computation circuit, and storage circuit of the pixel drivingchip, e.g., during powering up of the pixel structure for image display.Optionally, the shutdown circuit is configured to shut down theacquisition circuit, computation circuit, and storage circuit after theaforementioned compensation voltage is obtained and stored.

The pixel driving chip of FIG. 2 has several advantages. Even though thethreshold voltage of the driving transistor slowly drifts over time, itmay still maintain a relatively stable value over a certain continuousworking time. For example, in some embodiments, during a continuousworking time from powering up to shutting down, a single compensationvoltage may be sufficient to achieve satisfactory voltage compensationaccuracy in a display apparatus having the pixel driving chip describedherein. By using a single compensation voltage in the time period frompowering up to shutting down, consumption of time and processingresource may be significantly reduced as compared to an embodimentrequiring more frequent acquisition of compensation voltage values.Valuable processing resource may be allocated to display dataprocessing. Display delay may be avoided and display quality enhanced.

Optionally, the compensation voltage is a threshold voltage of thedriving transistor. Optionally, the compensation voltage is a voltagedrop at the source electrode of the driving transistor relative to apower-supply voltage Vdd. Optionally, the compensation voltage includesboth the threshold voltage of the driving transistor and the voltagedrop at the source electrode of the driving transistor relative to apower-supply voltage Vdd. For example, the pixel driving chip may beconfigured to compensate one or both of a gate scanning signal and adata signal.

In some embodiments, the compensation voltage is a threshold voltage ofthe driving transistor, i.e., the pixel driving chip is configured tocompensate the gate scanning signal. FIG. 3 is a circuit diagram of apixel structure during measurement of threshold voltage of a drivingtransistor according to some embodiments of the present disclosure. Inorder to measure a threshold voltage of a driving transistor (in thepixel structure), at least two test signals are needed to output to thedriving transistor, as shown in FIG. 3. A first test signal V1 is onevoltage excitation signal outputted to a gate of the driving transistorT4. A second test signal V2 is another voltage excitation signaloutputted to a drain electrode of the driving transistor T4. Byadjusting values of V1 and V2, it is able to control the drivingtransistor to be in a testing state so that various values of thethreshold voltage Vth (equal to a gate voltage minus a drain voltage)can be acquired.

Optionally, when a first switching unit (which is referred as a thinfilm transistor T1 in FIG. 3) is in a conduction state as controlled bya scanning signal Gate and a second switching unit (which is referred asanother thin film transistor T2 in FIG. 3) is in a conduction state ascontrolled by a sensor signal S, the first test signal V1 and the secondtest signal V2 are respectively passed to the gate and the drain of thedriving transistor T4. During this phase, the thin film transistor T5connected between the power-supply Vdd and the source of the drivingtransistor T4 is set to be a blocking state by an emission controlsignal EM so that the power-supply voltage Vdd cannot be passed to thesource electrode of the driving transistor T4. An acquisition circuitcoupled to the source electrode of the driving transistor T4 acquires ameasured source voltage of the driving transistor under the control ofboth the first test signal V1 and the second test signal V2. A thresholdvoltage of the driving transistor T4 in this testing state may beobtained as the difference between the measured source voltage and thefirst test signal V1 passed onto the gate of T4.

The threshold voltage of a driving transistor may change within acertain range when the source voltage and drain voltage at the sourceelectrode and drain electrode change. In order to obtain a more accuratethreshold voltage of the driving transistor at a specific bias statewith different drain-source voltages, the pixel driving chip in someembodiments is configured to acquire multiple threshold voltagescorresponding to different source and drain voltages, and store theminto a storage circuit. During image display, one of the multiplethreshold voltages stored in the storage circuit may be selected basedon actual source and drain voltage in a specific frame of image. Byhaving this design, a more accurate voltage compensation may beachieved.

Referring to FIG. 1 and FIG. 2, a control circuit in the embodiments isconfigured to output multiple sets of voltage excitation signals havingdifferent values to the driving transistor. Each set of voltageexcitation signals is able to control the driving transistor to be in atesting state (e.g., a threshold voltage testing state). A storagecircuit in the pixel driving chip is configured to store each thresholdvoltage corresponding to each set of voltage excitation signals.

In some embodiments, the compensation circuit includes a matching unitconfigured to determine one set of voltage excitation signals out of themultiple sets of voltage excitation signals that matches with actualsource and drain voltage in the specific frame of image. For example, ineach frame of image, the source voltage is provided by a data signal.The matching unit is configured to determine one set (a matched set) ofvoltage excitation signals out of the multiple sets of voltageexcitation signals that matches with a data signal in a specific frameof image. Optionally, the matching is performed by selecting one set ofvoltage excitation signals out of the multiple sets of voltageexcitation signals that has a measured source voltage closest to theactual data signal provided at the source electrode in the specificframe of image. Optionally, the matching is performed by selecting oneset of voltage excitation signals out of the multiple sets of voltageexcitation signals that has a drain voltage closest to the drain voltageprovided at the drain electrode in the specific frame of image.Optionally, the drain voltage provided at the drain electrode in thespecific frame of image may be calculated based on the source voltageprovided at the source electrode and inherent physical parameters of thedriving transistor.

In some embodiments, the compensation circuit also includes acompensation unit configured to use the threshold voltage correspondingto the matched set of voltage excitation signal to perform voltagecompensation to the original signal (e.g., an original gate scanningsignal) to obtain a compensated signal (e.g., a compensated gatescanning signal).

Referring to FIG. 3, when the power-supply voltage Vdd is maintainedunchanged and a voltage signal applied to the gate of the drivingtransistor T4 (i.e., a gate scanning signal) is changed, the drainvoltage of T4 undergoes change corresponding to the changing gatevoltage. Optionally, the drain voltage has a one-to-one correspondencewith the voltage signal applied to the gate of T4. Thus, in someembodiments, by changing the first and second test signals V1 and V2,multiple sets of threshold voltages can be obtained. Each thresholdvoltage corresponds to a different Vds, i.e., drain-source voltagedifference of the driving transistor T4.

During a normal operation process of a display apparatus, a drainvoltage corresponding to any set of original signal (e.g., a gatescanning signal and a data signal) may be calculated based on inherentphysical parameters of the driving transistor, e.g., to obtain acalculated drain voltage. For example, a matched set may be determinedby conducting a search in the storage circuit to select a set of voltageexcitation signals having a second test signal V2 closest to thecalculated drain voltage. The threshold voltage corresponding to thematched set may be used for compensating the original signal to obtain acompensated signal.

In some embodiments, the matching unit determines a matched set out ofthe multiple sets of voltage excitation signals that matches with theoriginal signal. The compensation unit uses the threshold voltagecorresponding to the matched set to compensate the original signal toobtain the compensated signal.

In some embodiments, the compensation voltage is a voltage drop at thesource electrode of the driving transistor relative to a power-supplyvoltage Vdd, i.e., the pixel driving chip is configured to compensatethe data signal provided at the source electrode of the drivingtransistor. FIG. 4 is a circuit diagram of a pixel structure duringmeasurement of voltage drop across the driving transistor according tosome embodiments of the present disclosure. In order to measure avoltage drop at the source electrode of the driving transistor, at leasttwo test signals are needed to output to the driving transistor, asshown in FIG. 4. A third test signal V3 is outputted from the pixeldriving chip to the gate of the driving transistor T4. A fourth testsignal Vdd (i.e., a power-supply voltage signal) is outputted to thesource of the driving transistor T4. When the first switching unit(referred to as the first thin film transistor T1 in FIG. 4) is in aconduction state under the control of a scanning signal Gate, the thirdtest signal V3 is passed to the gate of the driving transistor T4. Underthe control of V3, the driving transistor T4 is set to be in a blockingstate. In the pixel driving chip as shown in FIG. 4, the secondswitching unit, e.g., the thin film transistor T2, is not involved inthis compensation scheme. When a third switching unit (referred to asthe fifth thin film transistor T5 in FIG. 4) is in a conduction stateunder the control of an emission control signal Em, the power-supplyvoltage signal Vdd is applied to the source of the driving transistorT4. Thus, the acquisition circuit in the pixel driving chip can obtainthe measured source voltage at the source of the driving transistor T4.Optionally, measured source voltages for all driving transistors of allpixel structures of a display apparatus are obtained by the acquisitioncircuit.

In some embodiments, by comparing the measured source voltages of allpixel structures, a voltage drop at the source of the driving transistorrelative to the power-supply voltage can be obtained. Optionally, thevoltage drop of the source of the driving transistor relative to thepower-supply voltage is determined as a difference between the measuredsource voltage of the current one driving transistor and a referencesource voltage value. The reference source voltage value may be anyappropriate value. For example, the reference source voltage value maybe a maximum value among all measured source voltages of all drivingtransistors in all pixel structures. Optionally, the reference sourcevoltage value is a minimum value among all measured source voltages ofall driving transistors in all pixel structures. Optionally, thereference source voltage value is a medium or average value among allmeasured source voltages of all driving transistors in all pixelstructures.

In some embodiments, the one or more voltage excitation signals furtherincludes a fourth test signal V4. Referring to FIG. 4, in the aboveembodiment with the compensation voltage being the voltage drop, a clearsignal V4 may be applied to the drain of the driving transistor fordischarging cathode voltage of the light-emitting device. Specifically,a control signal S may be set to make the second transistor T2 in aconduction state, the test signal V4 passes from the pixel driving chipto the drain of the driving transistor T4. The test signal V4 is able todischarge cathode voltage of a light-emitting (diode) device to obtainmore accurate measurement results of the measured source voltage.

As shown in FIG. 3 and FIG. 4, at least two voltage excitation signalsare needed to obtain a compensation voltage (e.g., a threshold voltageor a voltage drop). As shown in FIG. 4, when measuring the voltage drop,the driving transistor T4 is set to a blocking state. To minimize thenumber of the voltage excitation signals, in a specific embodiment, thedriving transistor is a P-type transistor and the third test signal V3is the same as the power-supply voltage signal Vdd (e.g., the third testsignal V3 is multiplexed as the power-supply voltage signal Vdd).

In another aspect, the present disclosure provides a method of driving apixel structure including a driving transistor having a drain electrodecoupled to a light-emitting device. FIG. 5 is a flow chart illustratinga method for driving a pixel structure with voltage compensationaccording to an embodiment of the present disclosure. Referring to FIG.5, the method in the embodiment includes generating one or more voltageexcitation signals to control the driving transistor to be in acorresponding testing state; acquiring a measured source voltage at asource electrode of the driving transistor under the testing statecorresponding to the one or more voltage excitation signals; computing acompensation voltage based on the measured source voltage; storing thecompensation voltage; compensating an original signal provided to thedriving transistor using the compensation voltage to obtain acompensated signal; and outputting the compensated signal to the drivingtransistor.

In some embodiments, the original signal is a gate scanning signal, thecompensated signal is a compensated gate scanning signal, and the outputcircuit is configured to output the compensated gate scanning signal toa gate of the driving transistor. Optionally, the compensation voltageis a threshold voltage of the driving transistor. The one or morevoltage excitation signals includes a first test signal V1 outputted toa gate of the driving transistor and a second test signal V2 outputtedto a drain electrode of the driving transistor to control the drivingtransistor to be in a testing state. The threshold voltage is determinedas a difference between the measured source voltage and the first testsignal V1.

In some embodiments, the compensation voltage is a threshold voltage ofthe driving transistor, the step of generating one or more voltageexcitation signals includes generating a plurality sets of the firsttest signal V1 and the second test signal V2 to control the drivingtransistor to be in corresponding threshold voltage testing states.Optionally, the step of storing the compensation voltage includesstoring a threshold voltage corresponding to each set of the first testsignal V1 and the second test signal V2. Optionally, the method furtherincludes determining a matched set out of the plurality sets of thefirst test signal V1 and the second test signal V2 that matches with theoriginal signal; and using the threshold voltage corresponding to thematched set to compensate the original signal to obtain the compensatedsignal.

Referring to FIG. 5, in a specific embodiment when the compensationvoltage is a threshold voltage of the driving transistor, the voltageexcitation signals include the first test signal V1 outputted to thegate of the driving transistor and the second test signal V2 outputtedto the drain of the driving transistor. Both of the two test signals areused to control the driving transistor to be in a threshold testingstate. A measured source voltage is obtained. By varying at least one ofthe two test signals, different threshold voltages of the drivingtransistor can be obtained. The threshold voltage of the drivingtransistor is a difference between the measured source voltage and thevoltage of the first test signal V1.

Referring to FIG. 5, the control process of the driving method includesgenerating and outputting multiple sets of voltage excitation signals tothe driving transistor. Each set of voltage excitation signals is ableto control the driving transistor to be in the threshold testing state.The storage process of the driving method includes storing eachthreshold voltage corresponding to each set of voltage excitationsignals. The compensation process includes determining one set ofvoltage excitation signals out of the multiple sets of voltageexcitation signals that matches with the original signal, computing athreshold voltage corresponding to the one set of voltage excitationsignals, and using the threshold voltage to perform a voltagecompensation on the original signal to obtain a compensated signal.

In some embodiments, the original signal is a data signal, thecompensated signal is a compensated data signal, and the output circuitis configured to output the compensated data signal to the sourceelectrode of the driving transistor. Optionally, the compensationvoltage is a voltage drop at the source electrode of the drivingtransistor relative to a power-supply voltage Vdd. The voltageexcitation signal comprises a third test signal V3 outputted to a gateof the driving transistor and the power-supply voltage signal Vddapplied to the source of the driving transistor to control the drivingtransistor to be in a blocking state. The voltage drop is determined asa difference between the measured source voltage of the drivingtransistor and a reference source voltage value. The reference sourcevoltage value may be any appropriate value. For example, the referencesource voltage value may be a maximum value among all measured sourcevoltages of all driving transistors in all pixel structures. Optionally,the reference source voltage value is a minimum value among all measuredsource voltages of all driving transistors in all pixel structures.Optionally, the reference source voltage value is a medium or averagevalue among all measured source voltages of all driving transistors inall pixel structures.

Referring to FIG. 5, in a specific embodiment when the compensationvoltage is determined to be a voltage drop, the voltage excitationsignals include the third test signal V3 outputted to the gate of thedriving transistor and the power-supply voltage Vdd outputted to thesource of the driving transistor. Both of these signals are used tocontrol the driving transistor to be in a blocking state. A measuredsource voltage is obtained for each of all pixel structures of entiredisplay apparatus. The voltage drop at the source of the drivingtransistor relative to the power-supply voltage can be obtained as adifference between the measured source voltage for this drivingtransistor and a reference source voltage value.

Optionally, the driving transistor is a P-type transistor and the thirdtest signal V3 is the same as the power-supply voltage signal Vdd, e.g.,the third test signal V3 is multiplexed as the power-supply voltagesignal Vdd. Optionally, the voltage excitation signal further includes afourth test signal V4. Optionally, the method further includesdischarging cathode voltage of the light-emitting device by applying thefourth test signal V4 to the drain of the driving transistor. Forexample, the voltage excitation signals further include a clear signalV4 outputted to the drain of the driving transistor. The clear signal V4is configured to clear cathode voltage of the light-emitting device thatis coupled to the drain of the driving transistor within the pixelstructure.

In some embodiments, the method further includes a step of triggeringfor triggering processes of acquiring the measured source voltage,computing the compensation voltage based on the measured source voltage,and storing the compensation voltage during powering up of the pixelstructure for image display. Optionally, the method further includes astep of ending for ending the processes of acquiring the measured sourcevoltage, computing the compensation voltage based on the measured sourcevoltage, and storing the compensation voltage after storing thecompensation voltage to a storage circuit.

In order to implement the voltage compensation to improve image displayperformance of an active matrix organic light-emitting device, aspecific embodiment of the present disclosure provides a pixel structureincluding a light-emitting device (an OLED diode) coupled to a drivingtransistor T4. FIG. 6 is a simplified block diagram of a pixel structureaccording to the embodiment of the present disclosure. Referring to FIG.6, the pixel structure includes a state control circuit coupled to thedriving transistor T4. The state control circuit is coupled to a pixeldriving chip to receive one or more voltage excitation signals and isconfigured to use the one or more voltage excitation signals to controlthe driving transistor T4 to be in a corresponding testing state. Duringa normal operation period of the pixel structure, the driving transistorhas a gate receiving a compensated signal that is compensated over anoriginal signal by a compensation voltage. The compensation voltage isobtained based on the measured source voltages acquired at the source ofthe driving transistor under the testing state corresponding to variousvalues of the one or more voltage excitation signals. Optionally, thecompensation voltage is a threshold voltage of the driving transistor.Optionally, the compensation voltage is a voltage drop at the source ofthe driving transistor relative to a power-supply voltage.

FIG. 7 is a diagram of a pixel structure controlled by a pixel drivingchip operated during a threshold voltage compensation according to anembodiment of the present disclosure. Referring to FIG. 7, the voltageexcitation signals include a first test signal V1 and a second testsignal V2, outputted from the pixel driving chip. Optionally, thecompensation voltage is a threshold voltage of the driving transistor,the state control circuit in FIG. 6 includes a first switching unitwhich is the thin film transistor T1 in FIG. 7. The first switching unithas a first terminal coupled to the pixel driving chip for receiving thefirst test signal V1 outputted from the pixel driving chip. The firstswitching unit has a second terminal coupled to a gate of the drivingtransistor T4.

Referring to FIG. 7, the state control circuit includes a secondswitching unit which is the thin film transistor T2 in FIG. 7. Thesecond switching unit has a first terminal coupled to the pixel drivingchip to receive the second test signal V2 outputted from the pixeldriving chip. The second switching unit has a second terminal connectedto a drain electrode of the driving transistor T4.

Each of the first switching unit T1 and the second switching unit T2 hasa control terminal coupled to the pixel driving chip for receiving acontrol signal to control on and off states of T and T2. Specifically,the first switching unit T1 is controlled by a scanning signal Gate andthe second switching unit T2 is controlled by a sensor signal S. In someembodiments, the measured source voltage is acquired and the thresholdvoltage of the driving transistor T4 is determined as a differencebetween the measured source voltage (measured at the source of thedriving transistor) and a voltage value associated with the first testsignal V1 passed to the gate of the driving transistor T4.

FIG. 8 is a diagram of a pixel structure controlled by a pixel drivingchip operated during a voltage drop compensation according to anembodiment of the present disclosure. Referring to FIG. 8, the voltageexcitation signals include a third test signal V3 and a power-supplyvoltage Vdd, outputted from the pixel driving chip. Optionally, thecompensation voltage is a voltage drop at the source of the drivingtransistor relative to a power-supply voltage signal, the state controlcircuit of FIG. 6 includes a first switching unit which is the thin filmtransistor T1 in FIG. 8. The first switching unit T1 has a firstterminal connected to the pixel driving chip for receiving the thirdtest signal V3 and a second terminal connected to the gate of thedriving transistor T4. Moreover, the state control circuit includes athird switching unit which is the thin film transistor T5 in FIG. 8. Thethird switching unit T5 has a first terminal connected to the pixeldriving chip for receiving the power-supply voltage Vdd and a secondterminal connected to the source of the driving transistor T4.

Each of the first switching unit T1 and the third switching unit T5 hasa control terminal connected to the pixel driving chip for receiving acontrol signal to control on and off states of T1 and T5. Specifically,the first switching unit T1 is controlled by a scanning signal Gate topass the third test signal V3 to the gate of the driving transistor.When the third test signal V3 is passed to the gate of the drivingtransistor, it controls the driving transistor to be in a blockingstate. The third switching unit T5 is controlled by an emission controlsignal Em to allow a voltage drop relative to the power-supply voltageVdd at the source of the driving transistor T4. The driving transistorT4 is blocked. Optionally, the driving transistor T4 is chosen to be aP-type transistor, and the power-supply voltage Vdd may be used as thethird test signal V3.

Further in FIG. 8, the state control circuit includes a second switchingunit which is the thin film transistor T2. The second switching unit T2has a first terminal connected to the pixel driving chip to receive aclear signal V4 that is used for clearing cathode voltage of thelight-emitting device within the pixel structure. The second switchingunit T2 as a second terminal connected to the drain of the drivingtransistor T4. The second switching unit T2 has a control terminalconnected to the pixel driving chip for receiving a control signal S.The control signal S controls the on and off states of T2. Optionally,the control signal S in FIG. 8 may be provided by a same signal linethat provides the sensor signal S for controlling the transistor T2 inFIG. 7. Optionally, the control signal S is a same signal as the sensorsignal S.

In some embodiments, the state control circuit of FIG. 7 may furtherinclude a fourth switch unit which is the thin film transistor T3 shownin FIG. 8. The fourth switching unit T3 is controlled by a controlsignal S from the pixel driving chip for switching on or off. Forexample, during a sampling phase, the fourth switching unit T3 is set toa conduction state by the control signal S so that a measured sourcevoltage can be read by sampling measurement and acquired by the pixeldriving chip. While the pixel structure is in normal operation for imagedisplay, the fourth switching unit T3 is set to be in a blocking stateby the control signal S. In some embodiment, the control signal S may beprovided by a same signal line that provides the sensor signal S forcontrolling the transistor T2 in FIG. 7. Optionally, the control signalS is a same signal as the sensor signal S.

In some embodiments, the state control circuit may multiplex one or moreexisting thin film transistors in the pixel structure as one or moreswitching units for achieving desired state control. For example, one ormore existing thin film transistors may be used as thin film transistorsfor image display in a normal image display mode, and may be used asthin film transistors in the state control circuit in the signalcompensation mode.

FIG. 7 and FIG. 8 show two possible schemes for acquiring thresholdvoltages and voltage drops, respectively, at the source electrode of thedriving transistor when a threshold voltage (FIG. 7) or a voltage drop(FIG. 8) is used as a compensation voltage for compensating an originalsignal against the threshold voltage drift or variations of the voltagedrop at the source electrode of the driving transistor. In someembodiments, both the threshold voltage and the voltage drop at thesource electrode are compensated. FIG. 9 is a diagram of a pixelstructure controlled by a pixel driving chip operated for combinedthreshold voltage and voltage drop compensation according to anembodiment of the present disclosure. Referring to FIG. 9, the pixelstructure includes a light-emitting device coupled to a drivingtransistor T4. A pixel driving chip is configured to provide multiplesets of voltage excitation signals and control signals such as thescanning signal Gate, the sensor signal S, the emission control signalEM, the power-supply voltage Vdd, etc. A state control circuit includesa first switching unit T1, a second switching unit T2, a third switchingT5, and a fourth switching T3. The state control circuit is configuredto receive the multiple sets of voltage excitation signals from thepixel driving chip for controlling the driving transistor and samplingmeasured source voltages of the driving transistor at the correspondingtesting states. Further, the pixel driving chip is configured to computea compensation voltage based on the sampled measured source voltages,which is used for compensating an original signal against both thethreshold voltage drift of the driving transistor and variations of thevoltage drop at the source of the driving transistor relative to thepower-supply voltage so that a compensated signal can be outputted tothe driving transistor for controlling the light-emitting device withstabilized light emission.

Referring to FIG. 9, the first, second, third, and fourth switchingunits are substantially the same as those discussed in FIG. 7 and FIG.8, which are respectively provided as thin film transistors T1, T2, T3,and T5. Optionally, each of the thin film transistors T1, T2, T3, and T5is an N-type transistor. Optionally, each of the thin film transistorsT1, T2, T3, and T5 is a P-type transistor.

FIG. 10 is a simplified timing diagram for operating the pixel structureof FIG. 9 according to an embodiment of the present disclosure.Referring to FIG. 10, a driving operation of the pixel structure isillustrated by a timing diagram for each set of voltage excitationsignals including S, EM1, EM2, Gate1 (Gate2), and Vdt, outputted from anexternal pixel driving chip. FIG. 10 illustrates a drying operation of apixel structure in which the thin film transistors T1, T2, T3, and T5are all P-type transistors.

Referring to FIG. 9 and FIG. 10, signal Vdt is substantially equivalentof the V1 in FIG. 7 or V3 in FIG. 8. Signal Vi of FIG. 9 issubstantially equivalent of the V2 in FIG. 7 and V4 in FIG. 8.Optionally, the signal Vi is a fixed signal for clearing cathode voltageof light-emitting device (not included in the timing diagram of FIG.10). Signal Gate1 is provided to the control terminal of T1 in a currentrow of pixel sturctures of a display apparatus, signal Gate2 is thecontrol signal provided for a next row of pixel structures of the samedisplay apparatus. Signal EM2 is provided to a control terminal of anoptional transistor T6.

Referring to FIG. 9 and FIG. 10, in the P1 phase, the pixel driving chipacquires the threshold voltages of the driving transistor T4. Vdt isprovided as a signal Vf and is applied to a gate electrode of thedriving transistor T4. Vi is applied to a drain electrode of the drivingtransistor T4. Signal Gate1 (for current row of pixel structures) is ata low level, signal S is at the low level, and signal EM1 is at the highlevel. As a result, T1, T2, T3 are in conduction states and T5 is in ablocking state. As the source electrode of the driving transistor T4 hasa starting voltage at Vdd (at last image display phase), Vf controls thegate of the driving transistor T4 and Vi set the drain voltage of thedriving transistor T4. Therefore, source voltage Vs=Vf−Vth can beacquired by a sensor in the pixel driving chip via transistor T3, fromwhich the threshold voltage Vth is obtained. By changing Vf or Vi,different Vth values can be obtained at the conditions of differentdrain-source voltages Vds. This allows the effect of Vth be eliminatedthrough voltage compensation by selecting a matching Vth value as acompensation voltage. Additionally, the effect of Vth at specific Vdscan be eliminated to achieve even better compensation results. The Vivoltage is applied to the drain electrode of the driving transistor T4which is coupled to a cathode of an OLED diode and is able to dischargethe cathode voltage thereof.

In the P2 phase, EM1 and Gate1 signals are at low levels and signal S isat a high level. T1 and T5 are in conduction states, T2 and T3 are inblocking states. Power-supply voltage Vdd is applied at the same time tothe gate electrode and source electrode of the driving transistor T4 tocontrol it in a blocking state, thereby ending the process of acquiringvalues of threshold voltages Vth.

In the P3 phase, the pixel driving chip acquires the voltage drop at thesource of the driving transistor T4. Signal Gate1 is at low level,signal S is at low level, and EM1 is at low level. T5 is in a conductionstate to allow power-supply voltage Vdd to be written to the sourceelectrode of the driving transistor T4. In the P3 phase, the pixeldriving chip is able to read the source voltages for every pixelstructure as T3 is in conduction state. By comparing the source voltagemeasured at the source electrode of T4 with a reference source voltagevalue, the voltage drop at the source relative to Vdd may be determined,as discussed hereinthroughout. Optionally, Vi is applied to the drainelectrode of T4 for discharging OLED cathode voltage, leading toincreased accuracy in measuring the voltage drop at the source electrodeof T4.

In the P4 phase, the light-emitting device, or OLED, is operatednormally for emitting light for image display. In the P4 phase, signalEM1 is at low level, signal S is at high level, signal Gate1 is at lowlevel. The gate electrode of the driving transistor T4 is provided witha voltage Vg as Vdt=Vdt′+Vth−ΔVdd. The source voltage is provided with avoltage Vs=Vdd−ΔVdd. Therefore, the gate-source voltage Vgs of thedriving transistor T4 becomesVg-Vs=Vdt′+Vth−ΔVdd−(Vdd−ΔVdd)=Vdt′+Vth−Vdd. This leads to a draincurrent I=K(Vgs−Vth)²=K(Vdt′−Vdd)², which is independent from both thethreshold voltage Vth and the voltage drop ΔVdd. The OLED starts to emitlight as the driving current passes through. A substantially uniformpixel intensity throughout the display apparatus may be achievedsubstantially unaffected by Vth drift or voltage drop variations.

Optionally, a capacitor C is included in the circuit to have its firstterminal connected to the gate of the driving transistor T4 and a secondterminal connected to the source of the driving transistor T4. There isno charging or discharging path for the capacitor. Whenever the gateelectrode is floating, any change of the voltage at the source electrodewill be reflected to the gate electrode, e.g., the Vgs will remainunchanged. Or when Vdd is changing during this phase, there is no pathfor discharging the capacitance C. As a result, the Vgs remainsunchanged.

FIG. 11 is a simplified timing diagram for operating the pixel structureof FIG. 9 according to another embodiment of the present disclosure.Referring to FIG. 11, a shut-down operation can be applied to the firstswitching unit T1 prior to the start of the P4 phase, to eliminateeffects of voltage compensation sampling process in the P3 phase on thenormal display operartion in the P4 phase. As shown in FIG. 11, a shortpulse of high level signal is inserted for signal Gate1 so thattransistor T1 is turned off and only is turned on again by a low levelscanning signal Gate1 when the normal image display phase P4 starts.

For most AMOLED-based display apparatus (containing a plurality of pixelstructure and associated pixel driving chip according to the presentdisclosure), the source voltage of the driving transistor is uncertainduring a first frame of image when the display apparatus is powering up.The uncertainty of the source voltage of the driving transistor may leadto unstable image display. In some embodiments, a fifth switching unit(e.g., a thin film transistor T6 of FIG. 9) may be added between thedrain of the driving transistor and cathode of the OLED diode. A controlsignal EM2 is provided to the gate of T6. Prior to the P1 phase foracquiring measured source voltages, the signal EM2 is set at a highlevel in the P0 phase to turn off T6 and block the power supply from thelight-emitting device. In P0 phase, EM1 is at a low level to allowpower-supply voltage Vdd be applied to the source electrode of thedriving transistor to ensure stability of the source voltage of thedriving transistor. In later program phases (e.g., P2 and P3) andsubsequent normal display phase (e.g. P4), the T6 is turned on byapplying a low level EM2 signal. By having T6, the operation stabilityof pixel structure may be further enhanced.

The foregoing description of the embodiments of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formor to exemplary embodiments disclosed. Accordingly, the foregoingdescription should be regarded as illustrative rather than restrictive.Obviously, many modifications and variations will be apparent topractitioners skilled in this art. The embodiments are chosen anddescribed in order to best explain the principles of the invention andits best mode practical application, thereby to enable persons skilledin the art to understand the invention for various embodiments and withvarious modifications as are suited to the particular use orimplementation contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and their equivalentsin which all terms are meant in their broadest reasonable sense unlessotherwise indicated. Therefore, the term “the invention”, “the presentinvention” or the like does not necessarily limit the claim scope to aspecific embodiment, and the reference to exemplary embodiments of theinvention does not imply a limitation on the invention, and no suchlimitation is to be inferred. The invention is limited only by thespirit and scope of the appended claims. Moreover, these claims mayrefer to use “first”, “second”, etc. following with noun or element.Such terms should be understood as a nomenclature and should not beconstrued as giving the limitation on the number of the elementsmodified by such nomenclature unless specific number has been given. Anyadvantages and benefits described may not apply to all embodiments ofthe invention. It should be appreciated that variations may be made inthe embodiments described by persons skilled in the art withoutdeparting from the scope of the present invention as defined by thefollowing claims. Moreover, no element and component in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element or component is explicitly recited in the followingclaims.

1. A pixel driving chip for compensating an original signal provided toa pixel structure including a driving transistor having a drainelectrode coupled to a light-emitting device, the pixel driving chipcomprising: a control circuit configured to generate at least onecontrol voltage signals for controlling the driving transistor; anacquisition circuit configured to acquire a measured source voltage at asource electrode of the driving transistor under control of the at leastone control voltage signals; a computation circuit configured to computea compensation voltage based on the measured source voltage; a storagecircuit configured to store the compensation voltage; a compensationcircuit configured to compensate the original signal provided to thedriving transistor using the compensation voltage stored in the storagecircuit to obtain a compensated signal; and an output circuit configuredto output the compensated signal to the driving transistor for drivingthe light-emitting device.
 2. The pixel driving chip of claim 1, whereinthe original signal is one of a gate scanning signal provided to a gateelectrode of the driving transistor and a data signal provided to thesource electrode of the driving transistor.
 3. The pixel driving chip ofclaim 1, further comprising: a trigger circuit configured to triggeroperations of the acquisition circuit, the computation circuit, and thestorage circuit during powering up of the pixel structure for imagedisplay; and a shutdown circuit configured to shut down the acquisitioncircuit, the computation circuit, and the storage circuit after thecompensation voltage is computed and stored.
 4. The pixel driving chipof claim 1, wherein the compensated signal is a compensated gatescanning signal, and the output circuit is configured to output thecompensated gate scanning signal to a gate electrode of the drivingtransistor for image display; and the compensation voltage is athreshold voltage of the driving transistor, wherein the at least onecontrol voltage signals comprises a first test signal V1 outputted to agate electrode of the driving transistor to control the drivingtransistor to be in the conducting state and a second test signal V2outputted to a drain electrode of the driving transistor to control thedriving transistor, the threshold voltage being a difference between themeasured source voltage and the first test signal V1.
 5. The pixeldriving chip of claim 4, wherein the control circuit is configured togenerate the at least one control voltage signals multiple times, eachtime the at least one control voltage signals comprises a set of firsttest signal V1 and second test signal V2, thereby generating a pluralitysets of first test signal V1 and second test signal V2 having differentvoltage values; the storage circuit is configured to store a thresholdvoltage corresponding to each set of the plurality sets of controlvoltage signals for controlling the driving transistor; and thecompensation circuit is configured to determine a matched set out of theplurality sets of first test signal V1 and second test signal V2 thatmatches with the original signal, and is configured to compensate theoriginal signal using the threshold voltage corresponding to the matchedset to obtain the compensated signal.
 6. The pixel driving chip of claim5, wherein the second test signal V2 of the matched set is one that isclosest to a calculated drain voltage corresponding to the originalsignal, among a plurality of second test signals V2 of the pluralitysets of first test signal V1 and second test signal V2.
 7. The pixeldriving chip of claim 1, wherein the compensated signal is a compensateddata signal, and the output circuit is configured to output thecompensated data signal to the source electrode of the drivingtransistor for image display; and the compensation voltage is a voltagedrop at the source electrode of the driving transistor relative to areference voltage Vdd, wherein the at least one control voltage signalscomprises a third test signal V3 outputted to a gate electrode of thedriving transistor to control the driving transistor to be in a blockingstate and the reference voltage Vdd applied to the source of the drivingtransistor, the voltage drop being a difference between the measuredsource voltage of the driving transistor and a reference source voltagevalue.
 8. The pixel driving chip of claim 7, wherein the referencesource voltage value is one of a maximum value and a minimum value amongall measured source voltages of all driving transistors in all pixelstructures.
 9. (canceled)
 10. (canceled)
 11. A method of driving a pixelstructure including a driving transistor having a drain electrodecoupled to a light-emitting device, comprising: generating at least onecontrol voltage signals to control the driving transistor; acquiring ameasured source voltage at a source electrode of the driving transistorunder control of the at least one control voltage signals; computing acompensation voltage based on the measured source voltage; storing thecompensation voltage; compensating an original signal provided to thedriving transistor using the compensation voltage to obtain acompensated signal; and outputting the compensated signal to the drivingtransistor.
 12. (canceled)
 13. The method of claim 11, furthercomprising: triggering processes of acquiring the measured sourcevoltage, computing the compensation voltage based on the measured sourcevoltage, and storing the compensation voltage during powering up of thepixel structure for image display; and ending the processes of acquiringthe measured source voltage, computing the compensation voltage based onthe measured source voltage, and storing the compensation voltage afterthe compensation voltage is computed and stored.
 14. The method of claim11, wherein the compensated signal is a compensated gate scanningsignal, and the output circuit is configured to output the compensatedgate scanning signal to a gate electrode of the driving transistor forimage display; and the compensation voltage is a threshold voltage ofthe driving transistor, wherein the at least one control voltage signalscomprises a first test signal V1 outputted to a gate of the drivingtransistor to control the driving transistor to be in the conductingstate and a second test signal V2 outputted to a drain electrode of thedriving transistor to control the driving transistor, the thresholdvoltage being a difference between the measured source voltage and thefirst test signal V1.
 15. The method of claim 14, wherein generating theat least one control voltage signals comprises generating the at leastone control voltage signals multiple times, each time the at least onecontrol voltage signals comprises a set of first test signal V1 andsecond test signal V2, thereby generating a plurality sets of first testsignal V1 and second test signal V2 having different voltage values;storing the compensation voltage comprises storing a threshold voltagevalue corresponding to each control voltage signals; and compensatingthe original signal comprises determining a matched set out of theplurality sets of first test signal V1 and second test signal V2 thatmatches with the original signal; and using the threshold voltagecorresponding to the matched set to compensate the original signal toobtain the compensated signal.
 16. The method of claim 15, wherein thesecond test signal V2 of the matched set is one that is closest to acalculated drain voltage corresponding to the original signal, among aplurality of second test signals V2 of the plurality sets of the firsttest signal V1 and the second test signal V2.
 17. The method of claim11, wherein the compensated signal is a compensated data signal, and theoutput circuit is configured to output the compensated data signal tothe source electrode of the driving transistor for image display; andthe compensation voltage is a voltage drop at the source electrode ofthe driving transistor relative to a reference voltage Vdd, wherein theat least one control voltage signal comprises a third test signal V3outputted to a gate of the driving transistor to control the drivingtransistor to be in a blocking state and the reference voltage Vddapplied to the source of the driving transistor, the voltage drop beinga difference between the measured source voltage of the drivingtransistor and a reference source voltage value.
 18. The method of claim17, wherein the reference source voltage value is one of a maximum valueand a minimum value among all measured source voltages of all drivingtransistors in all pixel structures.
 19. (canceled)
 20. (canceled)
 21. Adisplay apparatus, comprising a pixel driving chip of claim 1; and apixel structure comprising: the light-emitting device; the drivingtransistor having the drain electrode coupled to the light-emittingdevice; and a state-control unit configured to be coupled between thepixel driving chip and the driving transistor for controlling thedriving transistor upon receiving the at least one control voltagesignals from the pixel driving chip; wherein the driving transistor isconfigured to receive the compensated signal for image display obtainedby compensating the original signal with the compensation voltage; thecompensation voltage is computed based on a measured source voltageacquired at a source electrode of the driving transistor under controlof the at least one control voltage signals.
 22. (canceled)
 23. Thedisplay apparatus of claim 20, wherein the compensated signal is acompensated gate scanning signal, and the output circuit is configuredto output the compensated gate scanning signal to a gate electrode ofthe driving transistor; the compensation voltage is a threshold voltageof the driving transistor, wherein the at least one control voltagesignals comprises a first test signal V1 and a second test signal V2;and the state-control unit comprises a first switching unit and a secondswitching unit, the first switching unit having a first terminalconfigured to be connected to the pixel driving chip for receiving thefirst test signal V1 and a second terminal connected to a gate of thedriving transistor, the second switching unit having a first terminalconfigured to be connected to the pixel driving chip for receiving thesecond test signal V2 and a second terminal connected to a drainelectrode of the driving transistor, each of the first switching unitand the second switching unit having a control terminal configured to becoupled to the pixel driving chip for switching on and off each of thefirst switching unit and the second switching unit, respectively, thethreshold voltage of the driving transistor being a difference betweenthe measured source voltage and the first test signal V1.
 24. Thedisplay apparatus of claim 20, wherein the compensated signal is acompensated data signal, and the output circuit is configured to outputthe compensated data signal to the source electrode of the drivingtransistor; the compensation voltage is a voltage drop at the sourceelectrode of the driving transistor relative to a reference voltage Vdd,wherein the set of control voltage signals comprises a third test signalV3 and the reference voltage Vdd; and the state-control unit comprises afirst switching unit and a third switching unit, the first switchingunit having a first terminal configured to be connected to the pixeldriving chip for receiving the third test signal V3 and a secondterminal connected to a gate of the driving transistor, the thirdswitching unit having a first terminal configured to be connected to thepixel driving chip for receiving the reference voltage Vdd and a secondterminal connected to the source electrode of the driving transistor,each of the first switching unit and the third switching unit having acontrol terminal coupled to the pixel driving chip for switching on andoff each of the first switching unit and the third switching unit,respectively.
 25. (canceled)
 26. The display apparatus of the claim 24,wherein the state control circuit further comprises a fourth switchingunit, the fourth switching unit comprising a thin film transistor havinga first terminal configured to be connected to the pixel driving chipfor receiving a clearing voltage signal V4 for discharging cathodevoltage of the light-emitting device and a second terminal connected toa drain electrode of the driving transistor, the fourth switching unithaving a control terminal configured to be connected to the pixeldriving chip for receiving a control signal for switching on and off thefourth switching unit.
 27. The display apparatus of claim 26, whereinthe pixel structure further comprises a fifth switching unit having athin film transistor coupled between the drain of the driving transistorand a cathode of the light-emitting device, the thin film transistor ofthe fifth switching unit having a control terminal configured to beconnected to the pixel driving chip for receiving a control signal, thecontrol signal being configured to turn off the thin film transistor ofthe fifth switching unit before the set of voltage signals is outputtedfrom the pixel driving chip to the driving transistor; and configured toturn on the thin film transistor of the fifth switching unit after theset of control voltage signals is outputted from the pixel driving chipto the driving transistor.